A fluid may comprise a mixture of fluids with different properties. For example, some fluids are liquids containing entrained gas, other fluids may combine liquids having different physical properties such as oil and water mixtures. Water removed from coal seams often contains entrained methane and other gases. Methane may partially separate from coal seam water during pumping. However, this partial separation may be inefficient in that entrained methane often remains in the water pumped from the seam. The entrained methane is a valuable commodity in and of itself. As is well known, methane is an efficient and environmentally friendly fuel, producing water and carbon dioxide when burned.
Methane left in water can create numerous problems. Water-laden methane requires additional chlorine demand in water disinfection systems. The increased use of chlorine in water treatment increases EPA-regulated by-products. Additionally, the colorless and odorless methane can be an explosion and fire hazard in water supplies. Pumping methane water can also be difficult because the methane can create gas locks.
Entrained methane can be removed from water by letting the water rest for an extended period of time. Such is often accomplished in an enclosed tank, with valves and/or piping that vent the methane evolved to the atmosphere or by placing the water in an open pond, as occurs in the coal bed methane fields in the Powder River Basin of Wyoming. At times the removal is enhanced by air sparging (adding air to the water) or by adding chemicals to the methane/water mixture. Because methane is odorless and colorless, it escapes unnoticed into the atmosphere.
Methane is known as a particularly damaging greenhouse gas. Methane takes years to breakdown naturally in the atmosphere. When it decomposes, it creates carbon dioxide, a greenhouse gas. Methane is over 20 times more effective at trapping heat in the atmosphere than carbon dioxide.
The amount of methane escaping into the atmosphere is significant. It is believed Powder River Basin coal bed methane wells are between 75% and 98% efficient in separating methane gas from pumped coal bed water. If existing Powder River Basin coal bed methane wells average 85% efficiency, 675,000 mcf of methane escapes into the atmosphere from just Powder River Basin wells each day.
Coal bed water is not the only fluid containing potentially harmful fluids. Entrained gases and volatile compounds may be found in polluted groundwater. For example, radon is a harmful gas that may be found in ground water. Additionally, hydrocarbon gases other than methane may also be found in ground water. It is undesirable to vent the entrained gases or compounds in polluted groundwater to the atmosphere because they may be toxic and may also contribute to greenhouse gas pollution.
Additionally, it may be desirable to separate mixtures of fluids having different physical properties. For example, crude oil spilled or released into water can cause significant environmental damage. The oil/water mixture may also contain gases. Also, motor oil, or other liquids, may be spilled or released into groundwater. Methods exist for removing such fluids from water but the known methods require significant energy input, are relatively inefficient and slow and may introduce harmful greenhouse gases into the atmosphere.
Currently used methods and apparatus for removing unwanted fluids from fluid mixtures are slow and relatively inefficient and often release unwanted greenhouse gases. Heretofore, efficient and cost effective methods and apparatus for removing unwanted fluids from fluid mixtures were not available. Although specific problems are described in this background section, the invention is not limited to solving these particular problems. Embodiments of the present invention may be useful in solving other problems not specifically described in this section. Thus, the background section should not be used to limit the scope of the appended claims.